Conventionally, as a mold clamping device and a mold clamping method of this type, there has been a ship-in molding device of a blow molding machine in which a component inserted into a molded article is fixed with a supporting rod, and then a parison is put on the component and mold clamping is performed from the outside of the parison as shown in, for example, Patent Document 1.
During the mold clamping described above, the movements of molds and the movement of a motor that supports a member inserted into a cavity are synchronized with each other. Although some constructions control the pressurization force of molds to make a film thickness uniform like the one shown in Patent Document 1, they do not synchronize positions.
Here, a description will be given of the outline of the device shown in Patent Document 1 described above together with its graphical representation.
In FIG. 11, reference signs 11, 11A show a pair of molds that forms a cuboid-like cavity. Pressing portions 31 are provided at the centers of the inner faces of the molds 11, 11A to be made slidable with respect to the molds by driving means 32 such as cylinders.
Reference sign 33 shows a parison made of thermoplastic resin serving as the raw material of a tank body. The parison is extruded from an extrusion molding machine after being heated to a predetermined temperature. Reference sign 35 shows a baffle plate made of resin in a rectangular shape placed within the tank body (not shown). The baffle plate 35 is horizontally supported at the tip end of a supporting rod 36 that does not have the function of a blow pin (i.e., is not cylindrical), and its both ends are arranged to face the pressing portions 31 of both of the molds 11, 11A, respectively.
In FIG. 12, reference sign 37 shows a blow pin arranged through one of the molds 11, 11A. The blow pin 37 is of a type that blows air by blowing means 38 of a cylinder, and its diameter is the same as the outer diameter of a hole (not shown) for an air breather formed on an upper face of the tank body (not shown).
As shown in FIG. 12, after the parison 33 is drawn down between the released molds 11, 11A to be fitted onto the baffle plate 35, the pressing portions 31 are first moved forward by the driving means 32 to press the facing lateral wall of the parison 33 and fix the ends of the baffle plate 35 to the inner face of the parison 33 by welding. At this time, the pressing force of the pressing portions 31 can be arbitrarily adjusted by the driving means 32. Then, the supporting rod 36 is removed from the molds 11, 11A after the completion of the welding.
Subsequently, as shown in FIG. 13, both of the molds 11, 11A are clamped to seal the upper and lower ends of the parison 33. At this time, the tip end of the blow pin 37 penetrates the lateral wall of the parison 33 to enter the inside of the parison 33. Then, compressed air is blown into the parison 33 from the tip end of the blow pin 37 to expand the parison 33 to closely adhere to the inner faces of the molds 11, 11A. Thus, a hollow body can be molded.
When molds are clamped as described above, an electric mold clamping device and a hydraulic mold clamping device are generally available as mold clamping devices for a blow molding machine.
The electric mold clamping device of a blow molding machine includes an opening/closing position detection mechanism and a synchronization device characterized by a mechanism that controls mold opening/closing positions by a main motor for driving molds and the operations of the servo motors of sub-motors in the molds and other places to enable the synchronization between mold opening/closing operations and the operations of the servo motors in the molds and other places.
Although some constructions control the pressurization force of molds to make a film thickness uniform like the construction shown in Patent Document 1, they do not synchronize positions.
As a conventional hydraulic mold clamping device described above, FIGS. 7 and 9 show a construction in which all platens 5 to 7 move in synchronization with each other. FIG. 7 shows a mold opening state, and FIG. 8 shows a mold clamping state.
That is, in FIG. 7, reference sign 1 shows a base, and first, second, and third linear-motion guides 2, 3, 4 formed from rails or the like and separated and independent from each other are provided on the base 1.
First, second, and third platens 5, 6, 7 are provided on the first, second, and third linear-motion guides 2, 3, 4, respectively, to be capable of linearly moving.
The first and third platens 5, 7 are fastened by a plurality of (actually four) tie bars 8 and fixed by respective nuts 9.
The respective tie bars 8 penetrate through-holes 6a and 7a of the second and third platens 6, 7 in an operable manner, and the second and third platens 6, 7 are configured to freely contact and separate from each other.
A hydraulic cylinder 12 in which a protrusion element 12A is configured to freely move in/out by a hydraulic unit 10 is provided on an inner surface 5a of the first platen 5.
The first and second molds 11, 11A are provided on inner surfaces 6A, 7A of the second and third platens 6, 7, respectively. An interlocking mechanism 15A based on a well-known rack-and-pinion in which L-shaped first and second levers 13, 14 and a gear 15 are combined together is provided beneath the second and third platens 6, 7.
An analog linear-motion detector 16 formed from a well-known linear scale or potentiometer for detecting the linear motion of the second platen 6 is provided on the base 1.
Note that the structures of the molds 11, 11A described above are not shown but are configured like, for example, the conventional example of FIGS. 11 and 12.
When the hydraulic cylinder 12 is operated via the hydraulic unit 10 in the mold opening state of FIG. 7 under the construction described above, the third movable platen 7 is pulled to the side of the second platen 6 via the interlocking mechanism 15A to bring the molds 11, 11A into press contact with each other to achieve mold clamping as the protrusion element 12A presses the second platen 6 to a right side in the figure.
The linear-motion state of the second platen 6 described above is detected as an analog value by the analog linear-motion detector 16.